1. Field of the Invention
The present invention relates to a solid-state image sensing device.
2. Description of the Related Art
In a solid-state image sensing device using a CMOS, an insulation film which covers a light-receiving region is formed from a transparent film so that light can reach the light-receiving region where incident light is converted into an electrical signal. For example, incident light passes through an oxide film having a refractive index of about 1.46 from air having a refractive index of about 1. The incident light enters a light-receiving region made of silicon having a refractive index of about 3 to 5. When light passes through the transparent film, it enters a substance having a high-refractive index from one having a low-refractive index. In accordance with the difference in refractive index, reflection occurs at the interface, decreasing the light incident efficiency in the light-receiving region. In a miniaturized solid-state image sensing device, the decrease in the quantity of light incident in the light-receiving region is a serious problem. A technique disclosed in Japanese Patent Laid-Open No. 2004-228425 increases the incident efficiency in the light-receiving region. For this purpose, a silicon nitride film having an intermediate refractive index between those of a silicon and silicon oxide film is stacked on an oxide film, reducing reflection of light. A technique disclosed in Japanese Patent Laid-Open No. 2004-221532 increases the sensitivity of a solid-state image sensing device. More specifically, an opening is formed in a light-transmitting film immediately above a light-receiving region and is filled with silicon oxide, forming a light guide.
However, the technique disclosed in Japanese Patent Laid-Open No. 2004-228425 cannot satisfactorily increase the transmittance because the same structure is applied to all light-receiving regions without considering the wavelength of incident light. Also, the technique disclosed in Japanese Patent Laid-Open No. 2004-221532 does not consider the wavelength of incident light. An aspect of the present invention, therefore, provides a technique of increasing the transmittance of an insulation film which covers a light-receiving region.